A torque converter incorporated in an automatic transmission to transmit an engine power output to a speed change mechanism comprises a pump adapted to be rotated integrally with a crankshaft of an engine, a turbine disposed opposed to the pump and adapted to be driven by the pump through fluid, and a stator disposed between the pump and the turbine and adapted to perform a torque amplifying function. In order to improve engine fuel economy, the torque converter may further comprise a lockup clutch adapted to be engaged so as to directly couple the pump and the turbine, except when the torque amplifying function is utilized, such as during vehicle starting, and when it is necessary to permit a relative rotation between the pump and the turbine, such as during speed changing. In this case, a lockup damper is provided on an input or output side of the lockup clutch to absorb shock during engagement of the lockup clutch.
As the torque converter having the above structure, there is a type disclosed in the following PTL 1. In this torque converter, a lockup clutch is disposed between a front cover defining a surface of a casing on the side of an engine and a turbine provided within the casing, and a lockup damper is disposed on a rear side of an outermost peripheral portion of the lockup clutch. Further, a damper spring of the lockup damper is disposed on the side of an outer circumference of the turbine, so that, as compared to cases where they are arranged in axially side-by-side relation, an axial dimension of the torque converter is suppressed.
However, in the torque converter disclosed in the PTL 1, the lockup clutch is a single plate type, which involves problems, such as limits to torque transmission capacity, and deterioration in controllability due to an increase in diameter of a clutch plate. Therefore, in recent years, a torque converter using a multi-plate type as a lockup clutch has been put to practical use, as disclosed in the following PTL 2.
In a torque converter disclosed in the PTL 2, a lockup damper is disposed in an outermost peripheral region of a space between a front cover and a turbine, and a multi-plate lockup clutch is disposed on an inner peripheral side of the space with respect to the lockup damper. Further, the lockup damper and the lockup clutch are arranged in an axially overlapping manner, so that an axial dimension of the torque converter is suppressed even using the multi-plate lockup clutch which has an axial dimension greater than that of the single plate type.